1. Field of the Invention
Montmorillonite, well-known for its large cation-exchange capacity and high swelling property, is utilized extensively in such applications as ion exchange substance and raw substance for pillared clay. When it is heated, it induces ion fixation and no longer retains usefulness because of consequent loss of its ion-exchange capacity.
2. Prior Art Statement
It is known that the cation-exchange capacity of montmorillonite which is well known as swellable clay decreases when this clay is subjected to a heat treatment. The reason for the decrease of the cation-exchange capacity may be that the interlayer exchangeable cations are caused by the heat to fix fast to the silicate layers and, as the result, the clay no longer retains the exchangeability. A method for controlling the cation-exchange capacity of montmorillonite by virtue of this phenomenon has been developed by the present inventors (Japanese Patent Application SHO 62(1987)-292629 correspond to U.S. application Ser. No. 07/394,969 and Japanese Patent Public Disclosure HEI 1(1989)-133918). A technique for restoring the cation-exchange capacity which has been decreased, however, remains yet to be established.
An object of this invention is to enhance the cation-exchange capacity of montmorillonite which has been decreased in consequence of fixation of ion.